Wide range sound film reproducing system



y 1952 w. J. ALBERSHEIM 2,602,351

WIDE RANGE SOUND FILM- REPRODUCING SYSTEM Filed July 8, 1950 INVENTOR ByWJ. ALBERSHE/M $7zrgw7 if ATTOR EV Patented July 8, 1 952 rs Hm.oF-FICE,

WIDE RANGE sounn FILMYREPRODUCING I I SYSTEM Walter J. Albersheini,Interlaken, N. J.,'assignor- 1 to Western Electric Company,Incorporated, New York, N. Y., a corporation oflNew York 5 ApplicationJuly 8, 1950, Serial No. 172,763

This invention; relates to sound film reproducing systems andparticularly to an improved wide frequency range reproducing systememploying a plurality of loudspeakers each of which ispredominantly'efiective in a' particular frequency range of theentire'range to be reproduced.

It is the objectof this invention to provide a size determined by theupper limit of the frequency range to be reproduced by its associatedloudspeaker.

A further feature of the'invention resides in the provision of means fordeflecting a portion of the modulated light beam to one ofthephotoelectric cells, which deflecting means is adjust able to advanceor retard the image projected to its associated photoelectric cellwith-respect to Y the same image projected to the other photoelectrio-cell' in order to adjust thephasing-and timing of the' sound reproducedby the'two loudspeakers."

I In wide frequency range'sound film reproduc ing systems usedheretofore it is necessary to use; an electrical dividing networkbetween the single photoelectric cell and the separate loudspeakers.

Iii-- addition to a; power loss introduced by such a dividing network,one of the loudspeaker units requires attenuation, as these two unitsare rarely of equal efiiciency. Consequently, the power amplifier mustcarry a combined signal load which is higher than that furnished totheloud-' speakers. The amplifier system including the transformers must becapable of passing the entire frequency range of approximately 7.3'

octaves. This reduces the load carryingcapacity of the transformers andcoilsthus increasing the number of amplifier stages with aconsequentincrease in low frequency phase distortion.

In asound filmreproducingsystem or the type discussed, the low frequencyasv'vellas the highfrequency speakers must be: placed: close to the In"order 'to obtain smoothprojection screen. I interaction between theoutputs of i the two loudspeakerhorns it is sometimes-necessary toshift} one speaker edge relative to the othersp'eak edge by 'asmallamOuntJ Natural reproductionf Claims. (01. 179-1003) posed infrontof the photoelectric cell assoici.

ated therewith. Means are provided for adi it the high and low frequencycomponentsofcomposite sound requires that the sounds of common originreach the ears simultaneously. Deviation from this requirement by morethan one fourhundredths of a second, or about'three feet" in speakerlength, produces unnatural tone quality in impact sounds, such aspercussion instruments. In order to meet this requirement, low frequencyloudspeakers in present-day wide range reproducing systems have beenshortened to the approximate length of the high frequency horn. 'Thisprecludes the desired use of the long folded horns for low frequencyreproduction whichhave a higher efficiency and quality.

In accordance with this invention the electrical. and acousticaldisadvantages of the present system of wide range reproduction'areeliminated by the provision of sucha reproducing system in which each ofthe loudspeakers is electrically connected to a separate photoelectriccell. Each of the photoelectric cells receiyes'the light-modu-v latedby. the sound track, one being positioned in the direct beamfrom thefilm and the'othei' positioned in the path of a portion of this beamwhichis deflected by a-mirror. The upperfre quency of the frequencyrange beingreproduced by the predominantly low frequency loudspeaker isdetermined by the width of an opticalslit dising the width of thisslitso that theassociated loudspeaker receives for reproduction only. cur;

rents of a frequency within the rangeof frequencies to be reproduced bythis loudspeaker-.

, To obtain phasing and; timing adjustments of Q one frequency componentof the composite soundswith respect to the other frequency component,the. angular position of the. deflecting mirror, which deflects aportion of the modulated light-beam to one of the photoelectric cells,is:- adjustable toadvance or retarduthezimage de i fiected to itsassociated? photoelectric cellwith;

projected to the other respect to the same image photoelectric cell.

It will be seen-thatby the use oi separate scanning slits inaccordancewith this invention;

the power consuming dividing network of the present system iseliminat'edi Each channel is provided with a 'separ'ate amplifier Vwhich has only to pass a frequency range of three or four octaves,'thuspermi-tting higher-" gain per stage and afniore economicaltransformer designi' No" intermodulation is likely where thehigh 'a ndlow frequencies are s'eparate'ly amplifiedand gain balance and'filtering can be donein'each channel at the low level amplifier stages.Also, the phasing and timing of high and low frequencies can beaccomplished by a simple adjustment of one scanning beam, thuspermitting the use of a low frequency loudspeaker of the long foldedtype giving higher quality sound reproduction while maintaining thespeaker edges in alignment at the projection screen or shifted relativeto each other by the small amount necessary to obtain smooth interactionbetween outputs.

In the drawing accompanying this specification, numeral l indicates aconstant intensity light source. A condenser lens 2 forms an image ofthe light source at or near the plane of the film F which bears thesound track to be reproduced. An objective lens 3 forms an image of thesound track on film F at a slit 4 which is formed by opaque plates 5 and6. The photoelectric cell receives the modulated light passing aperture4 and translates this light into electrical current. Numeral'S indicatesa. polarizing battery for the photoelectric cell 1. A condenser 9,resistance and inductance ll consti-- tute a high-pass filter in thecircuit from photoelectric cell 1 to an amplifier and gain control unitl2. A predominately high frequency loudspeaker I3 is electricallyconnected in the output of amplifier I2.

A portion of the modulated light beam is deflected by a mirror I4disposed between the objective lens 3 and slit 4. At the plane of theimage formed by the deflecting beam there is provided a slit [5 which isformed by opaque members [6 and IT. The width of a slit I5 may be variedby the slit-forming members It and I1. These members are adjustabletoward and away from each other by' means of threaded rods l8 and 19extending through internally threaded holes in a fixed housing indicatedat 20 and 2|. The end of each rod l8 and I9 is rotatably mountedin itsassociated slit-forming member to prevent rotation of these membersduring movement thereof toward and away from each other.

A photoelectric cell 22 receives the modulated light beam passingaperture l5 and converts this light into varying electrical current in acircuit including a polarizing battery 23, a lowpass filter includingcondenser 24, inductance 25 and resistance 26 and an amplifier and gaincontrol unit 21. In this system, a high quality folded horn 28 isconnected in the output from'amplifler 21.

In the system as shown in' the drawing the predominately high frequencyloudspeaker I3 and the predominately low frequency loudspeaker 21 areplaced immediately behind a projection screen with their edgessubstantially in the same plane. .A slight displacement of the edges asindicated in 30 may be necessary to obtain smooth acoustical interactionbetween the loudspeakers. This adjustment once made'is .permanent andthe phasing and timing of high and low frequency sound to compensate forthe difference in acoustical paths of the separate components of thecomposite sound is accomplished by adjustment of the scanning beam aswill be, explained hereinafter.

The mirror I4 is mounted on a pivot mounting (not shown) locatedsubstantially in a horizontal plane including the center lineof theoptical system.- The angle of deflectionof -mirror 14 may be changed toadvanceor retard the image 1 projected to photoelectric cell 22withrespect to the same image projected to photoelectric cell 1. Sincesound travels approximately 1100- feet per second in air and the film Ftravels at 18 inches per second, a mutual displacement of .001 inchbetween the scanning beams would be equivalent to a mutual displacementbetween the high and low frequency speaker diaphragms of .73 inch. Thus,if the distance from diaphragm to horn edge in the loudspeaker unit-28is ten feet greater than the distance between diaphragm and horn edge ofloudspeaker I3, the center of the image projected to slit l5 may beplaced ahead of the same image projected to slit 4 by .164 inch tocompensate for the difference in distance between the speaker diaphragmsand horn edges. In this manner, a high quality horn of the folded typeindicated at 28 may be employed and all sounds, including impact sounds,may be reproduced with natural tone quality.

While the light deflecting means is shown in the form of a mirror l4, itis within the scope of this invention to provide other optical means forsplitting the modulated beam and for adjusting the position of thedeflected beam relative to the other light beam.

The sound film reproducing system in accordance with this inventionincludes novel features offering definite advantages in a high quality,wide range sound film reproducing system.

What is claimed is:

l. A sound film reproducing system comprising a predominately highfrequency loudspeaker, a predominately low frequency loudspeaker, a pairof photoelectric cells each electrically connected to a separate one ofsaid loudspeakers, means producing a light beam modulated in accordancewith sound variations recorded on said film, means disposed in front ofeach photoelectric cell forming a scanning slit, means to adjust thewidth of one of said scanning slits in the direction of film motion, andmeans imaging difierent elemental areas of said modulated light beam atsaid scanning slits.

2. A sound reproducing system comprising a photographic film having asingle record of sounds recorded thereon, a predominately high frequencyloudspeaker, a predominately low frequency loudspeaker, a firstphotoelectric cell electrically con: nected to said high frequencyloudspeaker, ,a second photoelectric cell electrically connectedto saidlow frequency loudspeaker, means producing a light beam modulated inaccordance with sound variations recorded in the single record on saidfilm, means to project said light beam to said first photoelectric cell,means deflecting a selected elementalarea of said light beam to saidsecondphotoelectric cell, means forming a scanning slit in front of saidfirst photoelectric cell,

and means forming a scanning slit in front of said second photoelectriccell, said last-mentioned means being adjustable to vary the width of.saidv scanning slit formed thereby in the direction of film motion.

3. A sound film reproducing system in accord ance with claim 2 in whichthe position of said means deflecting a portion of said light beam tosaid second photoelectric cell is adjustable to ad,-'. vance or retardthe elemental area of said light-:

beam projected to said second photoelectric cell with respect to theelemental area of said lightbeam which is being simultaneouslyprojected'to said first photoelectric cell.-

cells being electrically connected to said high frequency loudspeakerand the other of said photoelectric cells being electrically connectedto said low frequency loudspeaker, optical means producing a light beammodulated in accordance with the sound variations recorded on said film,means for projecting said modulated light beam simultaneously to bothsaid photoelectric cells, means containing a scanning slit disposed in apath of the light beam to each of said photoelectric cells, one of saidscanning slits being wider in the direction of film motion than theother of said scanning slits, and adjustable light beam deflecting meansfor projecting onto one of said photoelectric cells an elemental area ofsaid light beam which precedes or follows an elemental area of saidlight beam being simultaneously projected onto the other of saidphotoelectric cells.

5. A sound film reproducing system comprising a predominately highfrequency loudspeaker, a predominately low frequency loudspeaker, a pairof photoelectric cells each electrically connected to a separate one ofsaid loudspeakers, means producing a light beam modulated in ac- WALTERJ. ALBERSHEIM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,901,033 Karolus Mar. 14, 19331,901,034 Karolus Mar. 14, 1933 1,950,011 Scheibell Mar. 6, 1934

